As an acoustic wave device using an acoustic wave, there has been known devices in which a piezoelectric substrate including an acoustic wave element formed thereon is bonded to a substrate located so as to have a cavity above the acoustic wave element with a frame surrounding the acoustic wave element. In such acoustic wave devices, there has been known a device in which the material of the piezoelectric substrate differs from the material of the substrate as disclosed in Japanese Patent Application Publication No. 2004-304622 (Patent Document 1), and a device in which the material of the piezoelectric substrate is the same as that of the substrate as disclosed in Japanese Patent Application Publication No. 2006-246112 (Patent Document 2). Additionally, there has been known a device in which an acoustic wave element is also formed on the substrate as disclosed in Japanese Patent Application Publication No. 2008-546207 (Patent Document 3). Furthermore, there has been known a thin film device in which an element is formed on at least one of two substrates, and the two substrates are bonded to each other with a resin as disclosed in Japanese Patent Application Publication No. 2005-109221 (Patent Document 4).
When the material of the piezoelectric substrate differs from that of the substrate as disclosed in Patent Document 1, stress is generated by the difference of linear expansion coefficients, decreasing the reliability of the acoustic wave device. When the material of the piezoelectric substrate is the same as that of the substrate as disclosed in Patent Document 2, the stress is reduced. However, the material of the substrate needs to be the same as that of the piezoelectric substrate such as a lithium tantalate substrate or a lithium niobate substrate, and thus it is difficult to achieve sufficient strength. The reliability of the acoustic wave device thus decreases.